Wash and peel the russet potatoes, then cut them into uniform cubes for even cooking. Place the cubes in salted boiling water and simmer until fork-tender, about 10 minutes. Drain thoroughly and return to the pot to steam-dry for a minute before mashing.

In the same pot of boiling water, add the chopped cabbage and sliced sweet onion and cook for 5 minutes to soften. Drain well and set aside.

Mash the drained potatoes until mostly smooth, then stir in the shredded Irish cheddar. Season with a pinch of salt and black pepper.

Lay out each tortilla and spread a dollop of Thousand Island dressing over one half.

On the dressed half of each tortilla, add a scoop of cheesy mashed potatoes, a layer of thinly sliced corned beef, and a portion of the cooked cabbage and onion. Fold the tortilla in half.

Heat oil in a skillet over medium-high heat. Fry the folded tacos, pressing gently, until golden brown on both sides, about 30 seconds per side.

Transfer the tacos to a paper-towel-lined plate to drain. Sprinkle freshly chopped chives over the top and serve warm.